Official Dynam 1500mm B-26 Marauder Thread

[rifleman_btx]

That pushed the battery back a half inch. I feel pretty good with that now

[Hardway]

Not cool at all.... :-(

[rifleman_btx]

And it did fly the first time, so I'm pretty confident that the CG wasn't allowing it to rotate up

[xviper]

and using the battery to get the CG.

By this do you mean going with a smaller battery? This plane is weird in that it "acts" nose heavy and hence, those weights in the tail end. If you leave them out, you may not be able to balance it well enough for it to fly right. My 4000mah and 3300mah batteries was as far as I could push them back and it still seemed nose heavy. I say "acts" and "seemed" because I needed quite a lot of UP elevator for it to fly level. If you are going to balance without the weights and only making adjustments to the battery, you may have to go down to a 3000mah or even much smaller to balance. I was thinking of maybe putting more weight in the tail but my last outing with the plane, it rotated in such a short distance that I suspect that it was the plush grass at the maidening field that caused the long take off run.

[rifleman_btx]

Viper, you are also running your cg in the 70-75 range correct? Mine at that point (70mm)actually felt tail heavy until I moved the battery up closer to the front. (First model pre-crash) it seemed to fly pretty well with even the 5000 until the second 5000 pack when it started going nuts on me. That's why I believed I had a crappy molding in my first one that crashed. Infact when I finished out the first 5000 pack it pulled a loop and rolled very well. Then all the sudden all hell broke loose.

[xviper]

I tried to balance it in between the recommended measurements (70 to 75mm) with the 4000mah battery, but it wouldn't quite balance. I couldn't push the battery back any further, so I just flew it as is and trimmed the ELE to make it fly level. By using my fingers on the mark I made (~72.5mm), it would nose down. To make it sit level (on my fingers) I'm guessing mine balanced at ~68mm. It flies quite well with either 4000mah or 3300mah, with that same UP elevator trim, so that's where I'm leaving it. In my second video, you could here one of the guys (who was also at the plush grass field with me) say how short a take off run that was compared to the first video.

[TiredIronGRB]

I tried to balance it in between the recommended measurements (70 to 75mm) with the 4000mah battery, but it wouldn't quite balance. I couldn't push the battery back any further, so I just flew it as is and trimmed the ELE to make it fly level. By using my fingers on the mark I made (~72.5mm), it would nose down. To make it sit level (on my fingers) I'm guessing mine balanced at ~68mm. It flies quite well with either 4000mah or 3300mah, with that same UP elevator trim, so that's where I'm leaving it. In my second video, you could here one of the guys (who was also at the plush grass field with me) say how short a take off run that was compared to the first video.

This is exactly how I have mine.

[rifleman_btx]

Indeed I remember that, just seems so odd that your feeling an nose heavy tendency and I was feeling tail heavy at about the same location with the batteries. As mine too were all the way back at first. Then when I moved them forward it flew better although yes I had to use bit of up trim to keep her level. I'm inclined to think that isn't weight causing the need for up trim but probably an angle issue with the horizontal stab. I might try to add some spacers under the rear mount of the tail feathers and see what happens. It sure is an interesting challenge.

[rifleman_btx]

After checking the angle, the rear of the tail is 3° low. I believe that our problem needs about a 2mm spacer under the rear of the tail

[CFIT rob]

Finished assembly, reglued flap hinges(glued one pushrod to underside of hinge..should have glued at half travel), repositioned some magnets to get wing cover fitting flush,did my my best to get wing seated into saddle,shimmed wing mounts down with some 1/8 ply to keep them below wing saddle surface(close but not perfect). Shaved outboard flaps to eliminate interference with alerons. Set high rates to suggested high rates. About 2mm up on ELE .Tried to set cg to 55mm as place to start. Using chinahobbyline 4000 40c 451g. Battery too far fwd to close hatch. Had to remove lead in tail. At 55mm cg, battery end is flush with fwd most part of front batt strap hold holder. Maiden today,5ish mph headwind. Take off half flaps (40ish yards,asphalt). Kept throttle 3/4 to full for first flight. Hade to give it most of my available up trim to fly level(55mm cg= nose heavy). No scary moments..flew approaches for a few min. Full flap landing felt very comfortable (kinda like my fw p38). Second flight went as well..except...stbd main stuck half up. Cycled gear multiple times, no effect. Landed without damage (except for the pucker factor). Cycled gear... works fine!?! Going to look for wiring issue. Going to move cg back to 60mm next flight. Plane looks so cool in the air, absolutley love it. Never thought i'd by flying a marauder...now where is my blackwidow?

[rifleman_btx]

Here's what I'm trying to see if my theory holds water

[themudduck]

How is your elevator neutral? Any uptrim?
Straight and level at speed what happens?

I had two more flights this evening, balanced at 55-57mm using my fingers. I still have just a little bit of up trim on the elevator for level flight, perhaps a little less than 1/8 inch. That is after I adjusted the incidence of the stab a little. (I like Rifleman's idea to put a little spacer to raise the TE of the stab. What I did was lower the LE just a little, by trimming the saddle.)

Straight and level at speed? Nothing happens, it just keeps going straight and level. If I point it 45 degrees up... then let go of the sticks, it keeps going at the same angle. Before I moved the balance point forward on Saturday, the model was tail heavy and when I went up at 45 degrees it rotated further up and went vertical by itself. If its nose heavy it will slowly nose over during this maneuver. This is a good test to check the CG.

Another flying test to test the CG: try flying inverted from level. If your plane is nose-heavy and is trimmed to fly level, when you invert it will nose towards the ground strongly. If your plane is tail heavy and trimmed to fly level, when you go inverted it will tend to go up without needing any down elevator. When I fly inverted with mine, I need to hold some down, but that's expected. It doesn't have a symmetrical wing and its normal to need some down when inverted.

Yesterday I settled at about 55-57mm (using my fingers, not a balancing machine). This evening on the second flight I tried moving the battery forward even further, a little forward of 55mm (perhaps 53mm) and at that point it was a little nose heavy but still flew very well. No problem with takeoff but I needed a little more up trim. At that position it just didn't want to flare for landing and I did a 3-point landing. At 55-57mm I am able to flare without a problem so I think that's where I like it best. I always use full flaps for landing.

Takeoffs have been very easy and scale-like (I have the flaps down about 1/4" inch for takeoff (maybe a little less than 10 degrees). Last weekend when it was balanced at 65mm, my takeoffs were more dramatic, it tended to jump off the ground suddenly and I had a nasty snap-roll tendency during high-speed flight. I'm sure it was tail heavy. If I were writing the manual, I would recommend 57, with a range of 55-60.

Rifleman I have no idea why your model is so much lighter. (I used a digital shipping scale on mine). And I don't know why yours wouldn't take off but I have an idea. A model with negative incidence (nose down) will be very difficult to take off. I'm using a 2.5" nose wheel and 2.75" Du-Bro mains. Mine sits on the ground just slightly nose-high (like the full-size Marauder)

[rifleman_btx]

Indeed the damn thing just keeps on rolling

[themudduck]

Here's a pic showing where I'm measuring the balance point. You're looking at the bottom, the nose is towards the right.

There's a "panel line" right at 60mm from the LE of the wing, on the bottom of the wing. That is what I am using for reference.
The "0" on the ruler is right on the line but the camera angle makes it look like its off.

I have my model balanced just forward of this line, say 55-57mm from the LE.

[borntoolate]

Here are the pics showing my changes to the pilots and nose gunner position

Nice job, Brent! You worked magic with those speedracers!

Bob

[ryramZ]

Here's a pic showing where I'm measuring the balance point. You're looking at the bottom, the nose is towards the right.

There's a "panel line" right at 60mm from the LE of the wing, on the bottom of the wing. That is what I am using for reference.
The "0" on the ruler is right on the line but the camera angle makes it look like its off.

I have my model balanced just forward of this line, say 55-57mm from the LE.

Yes, that line is what I showed in the video intro for the Flight Review. You have a slightly larger tire with the 3.5 nose wheel, 1/4" difference in tire equates to an 1/8" advantage. Sounds like you have it sorted nicely.

[themudduck]

Yes, that line is what I showed in the video intro for the Flight Review. You have a slightly larger tire with the 3.5 nose wheel, 1/4" difference in tire equates to an 1/8" advantage. Sounds like you have it sorted nicely.

That's right, my nose wheel is slightly bigger than stock. I had in mind to try and shorten the main gear a bit by taking out the retracts and working on the mount... but that's a lot of work so I decided the nose wheel would be easier. LOL

Anyway the nose wheel was just an experiment and it seems to be working for me. The stance just looks right.

Rifleman - here's a short video showing a takeoff yesterday from short grass, this is with the balance point at 60. See where my flaps are set. The video is only 1.5 minutes long, my cameraman lost the plane in the viewfinder after I chased after an "enemy aircraft" (a bird). https://www.dropbox.com/s/00wjmznerz...0%233.mp4?dl=0

[themudduck]

So here's my baby on the runway, with the slightly larger nose wheel and the rear hatch that still isn't adjusted at the back end! If you look closely you can see a tiny amount of "up" trim.

[rifleman_btx]

Indeed that's exactly what I was expecting out of mine today. The speed you had at lift off mine looked just a little faster than that even. I guess I did get the ***** of the bunch :/

[rifleman_btx]

I did balance it at 55, I'm going to 65 now plus I did change the incidence of the tail putting 3 mm of spacers under it just over the tail gunner position. When my new props come in I'll see what happens I also got the nose wheel off the stock p38 and now at least that part looks decent